Process of recovering organic compounds



March 2, 1948. J, s. HILL y `2,436,804

PROCESS 0F RECOVERING ORGANIC COMPOUNDS Filed July 19, l943 INVENT OR.

JOHN .SrANLe'Y4 l//LL ATTORNEY Parent-ed Mu. 2, 194s PROCESS F REC COMP John stanley um, uni-ei,

VERING ORGANIC OUNDS Miss., assigner to Maaonite Corporation, Laurel, Miss., a corporation oi Delaware Application .my 19. 194s, serial No. 495.383

' 11 claims. (c1. 26o-341) v 'I'his invention relates to an improvement in the production oi' furfural and organic acids, such as acetic and formic acids, from organic materials containing pentosans, hexosans and similar `com pounds by the acid hydrolysis of such materials, and is especially directed to the use of, and the results obtained by the use of, a salt brine in the manufacture of the above named products.

'I'he basic steps involved in making such prodl ucts comprise the acid digestion of the organic material containing pentosanshexosans and similar compounds. such as oat hulls, cottonseed hulls. liquorsfrom wood or other ligno-cellulose materials and containing pentosans, hexosans and similar compounds in solubleor dispersed or colloidal state, as described in U. S. Patent No. 2,224,135, and the like, disposition of remaining solids and/or of materials such as tars and the like which are present or formed during the digestion treatment, recovery of the furfural so produced, extraction of the mixed organic acids from the water present during the digestion, and iinally the separation and purincatlon of the organic acids.

By the addition of brine in the digesting step and utilizing the brine in this and subsequent steps, I am enabled to secure advantageous results in the several steps which are involved.

One object of the invention is the reduction of the time required for the digestion step and to secure improved digestion. Another object is to effect a more satisfactory separation of unreacted solids and/or tarswhich may be present or formed and like materials from the desired organic compounds. Another object is the pro- `vision of a process whereby brine-making salts and catalyst can be recovered and re-cycled and re-used i'or providing the brine for digestion of further materials containing pentosans. hexosans and the like.

One of the greatest difliculties heretofore-encountered has been inthe extraction of the organic acids from the water by the use of solvents, especially by solvents which are largely insoluble in water. With the use of suchV solvents an undesirably great quantity of solvent was required because of low partition coeillcients, that is to say, because the solubility of such acids in such solvents is low relative to the solubility of such acids in water. With the present 'invention solvents highly soluble in water can be used, thereby making the partition coefcients more favorable. and minimizing the amount of solvent needed.

One of the objects of making use of brine in accordance with the present invention is to reduce greatly the amount of solvent required to eiect the extraction of organic acids, from water.

Further objects of the invention will be made apparent by the following description.

When wood liquor such as described in U. S. Patent 2,224,135 is utilized, it is preferably convetted to a brine by the addition of a large amount of water soluble metal salts, preferably sodium salts, which are suiliciently stable to resist oxidation or reduction under conditions such as herein described, such for example as sodium chloride, sodium sulfate or the like. A saturated `solution of the salt material gives good results but so strong a-brine is not essential in all cases. Mineral aeid such as about 1-2% of sulfuric acid is added to the brine to act as a catalyst, with or without additional catalytic material such as .05.5% 0f aluminum sulfate. In case of I digestion of solid material such as wood, oat

hulls, cottonseed hulls and the like, the salt material is made into a brine with addition-of water.

The material containing pentosans, hexosans and similar compounds in brine is subjected to a hydrolysis or digestion treatment. Steam pressures of from p. s. i. to 1000 p. s. i. or over, and preferably about 20G-1000 p. s. i., may be satisfactorily used. The time required for my hydrolysis treatment can vary from about l or 2 hours for 60 p. s. i. to a fraction of a minute for 1000 p. s. i. 'I'he brine appears to aid in eil'ecting the reactions involved in the production of furfural from pentosans, and to reduce the time required for digestion treatment. When high steam pressures are used, the hydrolysis treatment is preferably terminated and solid materials subdivided by explosive discharge of the digestedmaterials.

During such discharge there will be a considerable hashing-off of furfural vapors and other low-boiling material such as volatile .organic acids, alcohol, acetone, etc., which may readily be collected and condensed. The liquor portion may then be treated. as by illtration, to remove the solids present or formed, as for example tars l 3 and the like. The salt appears to aid in this separation and a substantially clear brine can be obtained.

After suitable filtration, or even before, if so desired, the brine containing furiural, organic acids, etc., may be fed to a distilling column where the remaining furfural can be removed. If desired, a portion of the remaining organic acidcontaining briny liquid may be re-cycled to the digestion apparatus to build up the content of organic acid. Unduly great build-up oi organic acid content should be avoided, however, since the solvent recovery of organic acids hereinafter referred to has best application when the acid content is fairly low.

The brine solution material remaining after distilling olf furfural and containing organic acids is then subjected to solvent extraction treatment to recover the acids, preferably in an extraction column. Such extraction is preferably carried out by passing such brine solution into one end of a vertical extraction column, while passing the solvent in at the other end. With use of light organic solvents such as various alcohols. acetone or the like, having specific gravities which are less than that of water, the brine solution will be fed to the top of the extraction column.

In my extraction treatment solvents or mixtures of solvents are used which are infinitely soluble, or at least highly soluble, in water.' for example, ethyl or methyl alcohol, the propyl alcohols, acetone, methyl ethyl ketone, and the like, or mixtures thereof, Since these solvents are not very soluble in the brine, andthe organic acids are more soluble in the solvents than in the brine, the solvent takes up most of the acid together with a small part of the water from the brine. Thus the partition coefficients are very favorable to the solvents, and accordingly relatively small portions of solvent are required to eiect the extraction. The partition coefficient of methyl ethyl ketone, for example, was found to be several times the normal partition coefficient of about 0.8 of furfural which is the solvent generally preferred for use in the extraction of organic acids such as acetic and formic acids. The partition coenicient for acetone is even higher than for methyl ethyl ketone.

From the top of the extraction column there is obtained a liquid containing with the solvent the bulk of the organic acid material that was present in the brine solution, and some water. The acid concentration of this liquid has been found to be as high as 30% when using acetone, and as high as 65% when using methyl ethyl ketone, these gures based on the water-acid content not including the solvent. Y

As already noted, while the acid content of the brine may be built up by recycling after recovery of furfural and some build-up is useful, too great acid concentration is to be avoided since the solvents have less favorable partition coefficients when the acid content is unduly high.

present invention, the may be re-cycled to be re-used in the digestion step. If the material taken for digestion already contains much water, as will be the case when wood liquors, for example, are digested, it may be desirable to remove the water largely or entirely from the brine before re-using the salt and catalyst.

The invention will be more specifically illustrated by description in connection with the at. tached drawing which shows a flow sheet of one of the preferred embodiments of the method for the improved separation of the organic compounds i'rom the brine liquors.

Material containing pentosans, hexosans, and similar organic compounds, a brine solution, and a catalyst are fed to the digester Ill and subjected to a hydrolysis treatment, preferably by high pressure steam, to effect conversion of the organic compounds to various organic products such as furfural, organic acids or the like, Generally tars or tarry-like materials are also formed during the conversion.

The vcontents of the digester are discharged to the receiver I2 and furfura1 vapors are flashed oi to the furfural removing column I4. The brine liquor containing acids, and some furfural, may be recycled to the digester Ill in order to increase the acid concentration in the brine if Iso desired. If no recycling of the brine from the receiver is necessary. the liquor 1S Dumped into the furfural removing column I4 where the remaining portion of the furfural is removed. The furfural vapors which may include some entrained acids pass through condenser I6 and into the decanting unit I8. The entrained acids are recycled again into the column I4 and the furfural is then subjected to a dehydration action.

The tars or other insoluble materials may be removed from the brine containing furfural, organic acids, etc., before being fed into the furfural removing column by passing through a filter 28. It is, however, not necessary to remove the solids at this point of the cycle since the removal may be effected after the furfural has been removed.

After the furfural has been removed, the brinecontaining organic acids, etc., are fed to the acid removal column 20 4where solvents, such as acetone, contact the brine and the acids are extracted from the brine by means of the solvents. The solvents, as explained above, are very soluble in water but not very soluble in brine, and the organic acids are more soluble in the solvent than in the brine. As result of the different solubilities, the solvent and brine will separate into layers, the solvent layer containing most of the organic acids.

The solvent layer containing organic acids is then treated in a distillation column 22 to remove the solvent from the acids. The solvent is removed in the form of a vapor from the top of the column, passed through condenser 26, and fed back into acid extraction column 20.

The brine layer contains a quantity of solvent and this solvent is recovered by distilling off the solvent in column 24. The solvent vapors are moved with vapors coming from column 22 and then condensed in 26. If thecondensed solvents still contain entrained acids and/or brine after passing through the condenser 26, the condensed solvents may be refluxed in columns 22 or 24, for further purification of the solvent.

After the solvent has been recovered from the brine. the brine which still contains the catalyst catalyst-containing brin v originally addedin the digester is recycled to digester I0 for further use in the operation.

As an example to show the improved separation of organic acids from the brine liquor by means such asso C. or lower and containing NazSOs as the salt.

The importance of using organic solvents to obtain eiiicient separation oi' organic acids from If no brine solutions had been used in carrying out' the above procedures, such organic solvents as acetone could not have been used, since acetone isvvery soluble in water and no separation of acids from the hydrolyzed liquors could be made. Methyl ethyl ketone could have been used without using a brine solution, because this compound is not completely soluble in water, but the partition coefcient was considerably lower as compared to the partition coemcient when .the same solvent was used on digested liquors in brine. Furfural also shows an improved partition coefllcient when acid extractions are made from liquors containing such organic compounds in the presence of brine as compared to extractionsl from liquors without the addition of a brine solution.

In another example, digested liquor containing Na2SO4 was filtered, after which it was extracted with various solvents. 'Ihe following data show the results obtained: (The NaOH used for titration was 0.1033N) The temperature for these extractions was 29 C. I

oi' various organic solvents, the following data. are 5 brine solutions will thus be apparent; and, alpresented. In this example, digested liquor conthough the conditions or operation may be varied taining NaCl was filtered, after which it was exbroadly, I intend that such variations shall iall tracted with various solvents. The following data within the scope of the present claims. show the results obtained: (The NaOH used for I claim; titration was 0.1033N). `10 1. Process oi' manufacturing iurfural and or- IXgr Vol. Solvent Tg3?" .aqueous Layer Solvent Luyn Pm 1 29 `lecqoilec N'son 25 10 cc aeeton 29 1 co 1 cc.52g'cc. l 76 2""` '-soi'r Nion 29 1 eswgfaf 1 .alioif 1 11 3 25 l0 caluriural NO oc -O f h1 tn 1km 2o 1es=5aei '1=1lie% 1 s1 4...... ..5 l0 cc. met y e y ne....- o-H lo-H I 45 1 ce 1 i 5 25 10 00. atOllB y -o-H N-.OH

n ik :on -5 1 ec =4a`5cgc 1 sgc 1 71 6 25 l0 ce. methyl et y e e....- O N aoH. 'an 1o 1cc= 21536 l iccalgoo. 1in 7 25 guion Nuon 8.-.... 25 25 cc. methyl ethyl lretonem. 29 l cc.-.E6.7ge. 1 cc.'="6.7ge. 1.00

No salt (Mutual solubility high) NaOH ganic acids from material from which iurifural,V

acetic and formic acids can be produced, which comprises the steps oi incorporating watersoluble metal-salt brine with said material, subjecting said material to digestion with steam under pressure in the presence oi' an acid catalyst. condensing and recovering the iuriural produced,

treating the brine-containing organic acid with solvent highly soluble in water to separate the Vol. Liquor Vol. Solvent Aqueous Layer Solvent Loyer Pm 0c. 19 cc. l'ee. 1 25 10 cc. acetone 1 cci cc. 1 cia-:12.1 ce. 2.82

, NaOH NaOH 17.5 17.5 cc. 2 25 10 cc. ethanol... .3..- 1 cciii cc. l 5,510.5 ce. 1N

NaOH NaOH 23 cc. 12 ce. 3 25 10 ce. methyl ethyl ketone.-..- 1 0055.4 ce. l cc.=ll.5 ec. 2. 18

NaOH NaOH In the foregoing tables under the headings mixed organic acids from the brine. and recoveraqueous layer and solvent layer there are included, in addition to the volumes of the respective layers, titration igures for determination of organic acid content.

The partition coeilicient results obtained by using Na2SO4 are better than when using NaCl as the'salt in the brine. The partition coemcients will vary considerably with various salts as indicated above, and in some cases were as high as 8 ing the organic acids from the solvent.

4. Process as described in claim 3, in which the brine is recycled to the digestion step and the recovered organic solvent is recycled to the acidfrom-the-brine-separation step. l

5. Process of manufacturing furfural and organic acid from material from which furfural, acetic and formic acids can be produced by acid digestion,y the steps ot incorporating sodium whenusing acetone under favorable temperatures sulfate brine and an acid catalyst with the said ganic acids from material from which iuriural.

material, subjecting the mixture' to digestion with steam under pressure, condensing and recovering the furfural, extracting the mixed organic acids from the brine with acetone, and separating the organic acids from the acetone.

6. Process as described in claim in which the brine is recycled to the digestion step.

7. Process as described in claim 5, in which the brine is recycled to the digestion step and the recovered acetone is recycled to the acidfrom-the-brine-separation step.

8. In a process of manufacturing iurfural and organic acid from material from which furiurai, acetic and formic acids can be produced by acid digestion, the steps of incorporating sodium chloride brine and an acid catalyst with the said material, subjecting the mixture to digestion with steam under pressure, condensing and recovering the furfural, extracting the mixed organic acids from the brine by means oi a solvent which is highly soluble in water, and separating the acids from the solvent,

9. Process as described in claim 8, in which basato;

ganic acids from material from which furiural, acetic and formic acids can be produced by acid digestion, the steps of incorporating sodium sulfate brine and an acid catalyst with said material, subjecting the mixture to digestion with steam under pressure, condensing and recovering the furiural, extracting the mixed organic acids from the brine with methyl ethyl ketone, and separating the organic acids from the methyl ethyl ketone. Y

JOHN STANLEY HILL.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED s'rA'rEs PATENTS Number Name Date V2,078,241 Fulmer et al. apr. 27, 1937 2,369,655 Boehm Feb. 20, 1945 2,033,978 Dreyfus Mar. 17, 1936 1,996,706 Koster Apr. 2, 1935 FOREIGN PATENTS Number Country Date 495,116 France June 18, 1919 21,602 France Aug. 24, 1920 642,246 Germany Feb. 26, 1937 

